ROW MOVEMENT特性最初是在8i时引入的，其目的是提高分区表的灵活性——允许更新Partition Key。这一特性默认是关闭，只是在使用到一些特殊功能时会要求打开。除了之前提到的更新Partition Key，还有2个要求打开的ROW MOVEMENT的功能就是flushback table和Shrink Segment。所以，只有当使用到以上3个功能特性时，ROW MOVEMENT才会真正起作用。我们如果需要知道ROW MOVEMENT会对系统产生什么影响，就只要看这3个功能使用时会产生什么影响。
Flashback Table
先看Flashback Table。这一功能能帮助我们及时回滚一些误操作，防止数据意外丢失。在使用该功能之前，必须先打开ROW MOVEMENT，否则就会抛ORA-08189错误。我们看以下例子，可以说明在使用Flashback Table功能时，ROW MOVEMENT产生了什么作用：
SQL代码
SQL> create table test_move as select * from dba_users; Table created. SQL> select username, rowid from test_move; USERNAME ROWID ------------------------------ ------------------ DMP AAAwSfAAFAAAVlMAAA MYTBC AAAwSfAAFAAAVlMAAB CS2 AAAwSfAAFAAAVlMAAC TBC AAAwSfAAFAAAVlMAAD WOW AAAwSfAAFAAAVlMAAE REPO AAAwSfAAFAAAVlMAAF ... ... SYSTEM AAAwSfAAFAAAVlMAAk OUTLN AAAwSfAAFAAAVlMAAl 38 rows selected. SQL> delete from test_move where username = 'MYTBC'; 1 row deleted. SQL> commit; Commit complete. SQL> flashback table test_move to timestamp(systimestamp - interval '3' minute); flashback table test_move to timestamp(systimestamp - interval '3' minute) * ERROR at line 1: ORA-08189: cannot flashback the table because row movement is not enabled |
此时，由于ROW MOVEMENT还未打开，命令出错。继续完成演示：
SQL代码
SQL> alter table test_move enable row movement; Table altered. SQL> flashback table test_move to timestamp(systimestamp - interval '3' minute); Flashback complete. SQL> select username, rowid from test_move; USERNAME ROWID ------------------------------ ------------------ DMP AAAwSfAAFAAAVlMAAB MYTBC AAAwSfAAFAAAVlMAAm CS2 AAAwSfAAFAAAVlMAAn TBC AAAwSfAAFAAAVlMAAo WOW AAAwSfAAFAAAVlMAAp REPO AAAwSfAAFAAAVlMAAq ... ... SYSTEM AAAwSfAAFAAAVlMABJ OUTLN AAAwSfAAFAAAVlMABK 38 rows selected. |
